Excessive workplace heat exposures create well-known risks of heat stroke, and it limits the workers' capacity to sustain physical activity. There is very limited evidence available on how these effects reduce work productivity, while the quantitative relationship between heat and work productivity is an essential basis for climate change impact assessments. We measured hourly heat exposure in rice fields in West Bengal and recorded perceived health problems via interviews of 124 rice harvesters. In a sub-group (n=48) heart rate was recorded every minute in a standard work situation. Work productivity was recorded as hourly rice bundle collection output. The hourly heat levels (WBGT=Wet Bulb Globe Temperature) were 26-32°C (at air temperatures of 30-38°C), exceeding international standards. Most workers reported exhaustion and pain during work on hot days. Heart rate recovered quickly at low heat, but more slowly at high heat, indicating cardiovascular strain. The hourly number of rice bundles collected was significantly reduced at WBGT>26°C (approximately 5% per °C of increased WBGT). We conclude that high heat exposure in agriculture caused heat strain and reduced work productivity. This reduction will be exacerbated by climate change and may undermine the local economy.

Global climate change is projected to increase the frequency and duration of periods of extremely high temperatures. Both the general populace and public health authorities often underestimate the impact of high temperatures on human health. To highlight the vulnerable populations and illustrate approaches to minimization of health impacts of extreme heat, the authors reviewed the studies of heat-related morbidity and mortality for high-risk populations in the U.S. and Europe from 1958 to 2012. Heat exposure not only can cause heat exhaustion and heat stroke but also can exacerbate a wide range of medical conditions. Vulnerable populations, such as older adults; children; outdoor laborers; some racial and ethnic subgroups (particularly those with low SES); people with chronic diseases; and those who are socially or geographically isolated, have increased morbidity and mortality during extreme heat. In addition to ambient temperature, heat-related health hazards are exacerbated by air pollution, high humidity, and lack of air-conditioning. Consequently, a comprehensive approach to minimize the health effects of extreme heat is required and must address educating the public of the risks and optimizing heatwave response plans, which include improving access to environmentally controlled public havens, adaptation of social services to address the challenges required during extreme heat, and consistent monitoring of morbidity and mortality during periods of extreme temperatures.

The eye is said to be one of the most sensitive organs to microwave heating. According to previous studies, the possibility of microwave-induced cataract formation has been experimentally investigated in rabbit and monkey eyes, but not for the human eye due to ethical reasons. In the present study, the temperature elevation in the lens, the skin around the eye and the core temperature of numerical human and rabbit models for far-field and near-field exposures at 2.45 GHz are investigated. The temperature elevations in the human and rabbit models were compared with the threshold temperatures for inducing cataracts, thermal pain in the skin and reversible health effects such as heat exhaustion or heat stroke. For plane-wave exposure, the core temperature elevation is shown to be essential both in the human and in the rabbit models as suggested in the international guidelines and standards. For localised exposure of the human eye, the temperature elevation of the skin was essential, and the lens temperature did not reach its threshold for thermal pain. On the other hand, the lens temperature elevation was found to be dominant for the rabbit eye.

Both extreme heat and cold can be challenging for athletes during training and competition. One role of the team physician is to educate coaches and athletes on the risks of exposure to these conditions and how to best prevent and manage their adverse effects. Heat illness varies in degree from mild to severe, with the most severe forms being potentially fatal. Cold exposure can result in systemic effects and peripheral injury to the extremities.

Exercise-induced heat stroke is defined as core temperature greater than 104 degrees F (400 degrees C) accompanied by signs or symptoms of organ system failure, most commonly CNS dysfunction. Exertional heatstroke is a life-threatening emergency that requires immediate whole-body cooling for a satisfactory outcome. Cooling should be initiated and, in the absence of life-threatening complications, completed on site prior to evacuation to an emergency department or other facility. Cool-water immersion provides the fastest whole body cooling rate and the lowest morbidity and mortality for exertional heat stroke. When water immersion is unavailable, ice water towels combined with ice packs on the head, trunk, and extremities provide effective but slower whole-body cooling. Medications, including antipyretics and dantrolene, are not effective in treating heatstroke and should not be used. Clinical observations indicate that prognosis is closely linked to the amount of time a patient's temperature remains elevated. Prevention strategies are essential to reducing the incidence of exertional heatstroke, heat exhaustion, and exercise-associated muscle cramping.

International classification of heat illness including heat stroke, heat exhaustion, the others is well known. However, the new classification from the grade III(severe) to the grade I(mild) is more common in Japan. There is a good correlation between the two classifications. The Heatstroke Surveillance Committee of the Japanese Association for Acute Medicine has collected the data using the new classification. The outcome of patients who were mechanically ventilated due to heat illness was not affected by cooling procedures but independently associated with systolic blood pressure and SpO2 at the scene, and arterial base excess on admission.

In the type of heat illness, several medical terms such as heat syncope, heat cramp, heat exhaustion, heat stroke are included. But their Japanese medical terms are neither unified nor clearly defined. To eliminate this problem, the new classification for heat illness is proposed. By the severity of heat illness, they are divided into three grades. Grade I is corresponded to heat cramp and heat syncope. Grade III is corresponded to heat stroke, and used for any one of the three following clinical findings, (1) Central nervous system dysfunction, i.e., consciousness disturbance, seizure, ataxia. (2) Liver and kidney dysfunction. (3) Clotting disorder, i.e., DIC. This classification can be beneficial not only to the diagnosis in the hospital, but also to the early detection and management of heat illness in the field.

This study examined whether a rise in thermal and cardiovascular strain during exercise to exhaustion in the heat at different intensities is associated with compromised muscle and cerebral oxygenation. Using near-infrared spectroscopy, oxygenation changes in the vastus lateralis and prefrontal cortex of ten subjects cycling to exhaustion in 40 °C conditions at 60 % (H60%) and 75 % (H75%) maximal oxygen uptake (VO₂(max)) and for 60 min in 18 °C conditions at 60 % VO₂(max) (C60%) were examined. Thermoregulatory and cardiovascular responses were also monitored. Rectal temperature reached 38.1 °C in the C60% trial, 39.7 °C (~60 min) and 39.0 °C (~27 min) in the H60% and H75% trials, respectively (P < 0.001). The core-to-skin temperature gradient was similarly narrow (~0.9 °C) at exhaustion in the heat, occurring >97 % of maximum heart rate and accompanied by significant declines in stroke volume, cardiac output and mean arterial pressure (P < 0.01). Vastus lateralis oxygen saturation (SmO(2)) declined at the onset of exercise in all conditions, remaining similarly depressed at exhaustion in the heat. Prefrontal cortex oxygen saturation (ScO(2)) was ~10 % lower at exhaustion in the H60% and H75% trials compared with C60% (P < 0.01), which remained above baseline from 15 min onward. These findings indicate that changes in SmO(2) and ScO(2) are associated with the development of thermal and cardiovascular strain during exercise to exhaustion in the heat, which is accelerated by exercise intensity. In locomotor muscles, a potential reduction in oxygen delivery may develop, whereas in the brain, the progressive reduction in ScO(2) may induce mental fatigue.